Field of the Invention
The invention relates in general to a scanner, and more particularly to a sheet-fed scanner and image scanning method using the same.
Description of the Related Art
Existing scanners basically can be classified namely into two types, flatbed scanners and sheet-fed scanners. The flatbed scanner is subjected to many restrictions in terms of use, for example, the cover has to be manually lifted while using, a large volume of documents cannot be scanned automatically in one batch, the size of the flatbed scanner is extremely huge, and the scanning speed is not fast enough. The sheet-fed scanner, such as a name card scanner or a sheet-fed scanner capable of scanning name cards, photos and ordinary documents, advantageously has small volume, light weight and fast scanning speed, and can automatically scan a large volume of documents in one batch. Therefore, for those users requesting automatic document scanning, the sheet-fed scanner is a preferred choice.
However, in subsequent image processing such as automatic cropping and skew correction, the scanning background is required for identifying the boundary between the background image and the scanner document image before proceeding to the next stage of image processing. Since the flatbed scanner has a complete sheet of background sheet, the background sheet can be designed to have a special vein or pattern by which the image processing unit can easily identify the background image and the scan document image without worrying the situation that the background sheet may accidentally have the same color with the scanned document. In comparison, the background sheet of the sheet-fed scanner is strip-shaped, and the scanned region is merely a fixed scan line and cannot have a vein or pattern designed thereon. If the color of the background sheet is too close to that of the scanned document and cannot be used as a basis for identifying the document image and the background image, more delicate image processing cannot be performed. Consequently, the obtained image will have insufficient precision, size error, skewness or cropping mistakes.